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Officially, British exports to the EU would face an average tariff of two per cent, though the charge on food would be much higher.

If we could negotiate access via some sort of free trade agreement, as Norway and Switzerland have done, the tariff would be waived.
If not, devaluing sterling could lower the price of our goods, though this would be hard to pull off in today’s sophisticated capital markets.

The second variable is the future of the global economy. Is Europe in long-term decline and are we better off as a partner for the emerging giants, a trade hub – an Atlantic Hong Kong? Or is Europe capable of reinventing itself as an economic dynamo, just as it did after 1945?

Until these questions are answered, our balance sheet will be missing its last figure, whether plus or minus.